Radon in Arizona: radon map by county

EPA's Map of Radon Zones puts 0 of Arizona's 15 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 15 in Zone 2 and 0 in Zone 3. Of 2,229 building tests that radon laboratories reported for 2008 to 2017, 16.8% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 38 of 42 states with 1,000+ tests). The highest county share is Coconino County (30% of 153 tests).

counties in Zone 1 (above 4 pCi/L predicted)

counties in Zone 2 (2 to 4)

counties in Zone 3 (below 2)

16.8%

of 2,229 lab tests at or above 4 pCi/L

Radon by county in Arizona

EPA radon zone and radon test results for each county in Arizona
County	EPA zone	Lab tests	Median	4+ pCi/L
Apache County	Zone 2	1	1.9	0%
Cochise County	Zone 2	20	2.8	26.9%
Coconino County	Zone 2	153	2.3	30%
Gila County	Zone 2	8	5.7	64.7%
Graham County	Zone 2	6	3.0	36.4%
Greenlee County	Zone 2	n/a	n/a	n/a
La Paz County	Zone 2	n/a	n/a	n/a
Maricopa County	Zone 2	1,512	1.6	17.4%
Mohave County	Zone 2	24	0.2	4.1%
Navajo County	Zone 2	12	1.1	0%
Pima County	Zone 2	219	1.1	6.8%
Pinal County	Zone 2	74	0.9	8.9%
Santa Cruz County	Zone 2	5	1.7	0%
Yavapai County	Zone 2	187	1.6	16.2%
Yuma County	Zone 2	8	0.6	0%

Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).

What the zones mean

Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.

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Radon in Arizona: questions

What radon zone is Arizona?

EPA's 1993 map does not give states one zone; it zones each county. In Arizona, 0 counties are Zone 1, 15 Zone 2 and 0 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".

Which Arizona counties have the highest radon levels?

By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Coconino County 30% (median 2.3 pCi/L, 153 tests); Cochise County 26.9% (median 2.8 pCi/L, 20 tests); Maricopa County 17.4% (median 1.6 pCi/L, 1,512 tests); Yavapai County 16.2% (median 1.6 pCi/L, 187 tests); Pinal County 8.9% (median 0.9 pCi/L, 74 tests).

How common is high radon in Arizona?

16.8% of the 2,229 tests in the laboratory data for Arizona (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.

Should I test for radon in Arizona?

Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.

States bordering Arizona

Radon in California (2 of 58 in Zone 1)Radon in Nevada (9 of 17 in Zone 1)Radon in New Mexico (7 of 33 in Zone 1)Radon in Utah (7 of 29 in Zone 1)

Other free hazard lookups

All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).

Superfund sites in Arizona · Radon map of every state

Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.